This invention relates to an optical module for receiving light comprising a photoelectric transfer unit (hereinafter referred to as "photounit") packaged in a transparent resin molding and assembled in a connector housing, and more specifically to an optical module which can shield the photounit against electromagnetic waves with a simple structure.
Japanese Patent Publication 62-44828 and Japanese Utility Model Unexamined Publication 61-24705 teach means for protecting the photounit in a connector housing against electromagnetic waves.
In the former publication, a shield material having shielding properties against electromagnetic waves such as a layer of conductive film is laminated to the photounit covered with a transparent resin and the shield material layer is connected to a grounding pin of the photounit. Then the shield material layer is covered with an opaque resin layer.
In the latter publication, a metallized layer is formed on one side of a ceramic circuit board and a seal ring is secured to its edge. A metal shell is secured to the seal ring to seal the elements mounted on the board. The photounit thus made is put in a receptacle made of a conductive material so that the seal ring touches the receptacle. The shield against electromagnetic waves is provided by keeping namely the three members, the seal ring, the shell and the receptacle, at an AC grounding potential.
The technique disclosed in Japanese Patent Publication 62-44828 involves complicated manufacturing steps and thus is costly because transparent resin, shield material and opaque resin have to be laminated one on another.
The module disclosed in Japanese Utility Model Publication 61-24705, which uses a ceramic board, a seal ring, a metal shell and a conductive receptacle, is reliable. But the manufacturing steps are even more complicated than for the former module and its materials cost is too high to be acceptable.